“Tungsten steel” is a common term used to describe materials with exceptional mechanical properties, suggesting a strength far exceeding that of regular steel. While this perception of immense strength is accurate, the term itself can be misleading, covering two distinct material types with vastly different performance characteristics. These materials are heavily relied upon in demanding industrial applications, particularly for tools that must maintain their sharpness and integrity under extreme conditions. Understanding how strong tungsten-containing materials are requires examining their specific composition and the resulting mechanical trade-offs, including hardness, resistance to pulling forces, and susceptibility to sudden impact.
Defining Tungsten-Containing Materials
The umbrella term “tungsten steel” typically refers to two separate classes of engineering materials: Tungsten High-Speed Steel (HSS) and Tungsten Carbide (WC).
Tungsten High-Speed Steel is a genuine alloy, created by adding tungsten, molybdenum, chromium, and vanadium to molten iron and carbon. This process results in a homogeneous structure, often used for cutting tools like drill bits and taps, where a balance of hardness and toughness is required. Its tungsten content generally ranges from 5% to 20% of the material’s weight.
Tungsten Carbide, in contrast, is not technically a steel alloy but a cermet—a ceramic-metal composite. It is produced through powder metallurgy, where tungsten carbide powder is sintered with a metallic binder, usually cobalt. This forms a structure where extremely hard tungsten carbide particles are cemented together by the tougher metal binder. Tungsten carbide is the primary component, often exceeding 90% of the material’s mass, and is responsible for the material’s extreme performance.
The properties of a finished part depend entirely on which material is used. HSS is a true steel alloy designed for strength and resilience, while Tungsten Carbide is a composite engineered for maximum hardness and wear resistance.
The Hardness Factor
Hardness is the primary measure of strength for tungsten-containing materials, particularly when used as cutting and shaping tools. Hardness is defined as the material’s resistance to permanent indentation, scratching, and abrasion. Tungsten dramatically increases this property, making the material highly wear-resistant.
Tungsten High-Speed Steel (HSS) achieves a high Rockwell C (HRC) hardness, typically ranging between HRC 63 and HRC 67 after heat treatment. This is significantly harder than standard tool steels, helping HSS maintain a sharp cutting edge longer. The Vickers hardness for HSS is generally around 700 to 900 HV.
Tungsten Carbide exhibits a level of hardness that is vastly superior, second only to diamond. Its Vickers hardness values typically range from 1600 HV to 2200 HV, more than double that of high-speed steel. This extreme hardness allows carbide tools to cut materials that would quickly dull HSS, extending tool life significantly in abrasive environments. This exceptional resistance to wear makes it the material of choice for demanding applications like mining, drilling, and high-speed machining.
Comparing Tensile Strength and Brittleness
While tungsten materials excel in hardness, their overall strength profile must also account for tensile strength and toughness, revealing a critical trade-off. Tensile strength measures a material’s resistance to stretching or pulling forces before fracturing.
Tungsten High-Speed Steel maintains a good balance, offering improved tensile strength and yield strength over standard steels due to its fine-grained structure. It is significantly tougher than tungsten carbide, meaning it can absorb more impact energy without fracturing. This makes HSS suitable for applications involving intermittent cuts or mechanical shock, such as drill bits or saw blades.
Tungsten Carbide, despite its extreme hardness, is comparatively brittle. As a ceramic-metal composite, it has a lower resistance to sudden impact, which can cause it to chip or shatter easily. However, Tungsten Carbide possesses extremely high compressive strength—the ability to withstand crushing forces—which can be up to 6000 MPa, far exceeding that of most steels. This combination of high compressive strength and low impact resistance defines Tungsten Carbide’s strength profile.
How Tungsten Alters Steel’s Properties
Tungsten enhances steel properties primarily by acting as a powerful carbide-forming element. When added to steel, it combines with carbon to form extremely hard tungsten carbides within the steel’s microstructure. These microscopic carbide particles are significantly harder than the surrounding steel matrix.
The presence of these carbides provides the steel with superior wear resistance, as the hard particles resist abrasive forces. Tungsten also promotes a fine-grained structure in the steel matrix, which contributes to higher overall toughness for a given level of hardness.
The most notable effect of tungsten is the development of “hot hardness,” the ability to retain strength and hardness even at elevated temperatures. Tungsten carbides are highly stable and resist dissolving or allowing the steel’s grain structure to coarsen, even when friction generates temperatures above 500°C. This allows high-speed steel tools to operate at much faster cutting speeds than traditional carbon steels without softening or losing their cutting edge.